Posted on by Nancy Atkinson

James Elliot, Discoverer of Uranus Ring System, Dies

James Elliot, 1943–2011

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Astronomer James Elliot, a professor at MIT, has passed away at the age of 67. Elliot was part of a team of astronomers from Cornell University that discovered the rings around the planet Uranus in 1977. Elliot specialized in the techniques of planetary astronomy, particularly stellar occultations, to probe planetary atmospheres and the physical properties of small bodies in the outer solar system and beyond. Of particular interest to him was Pluto, Triton, Kuiper Belt objects and extrasolar planets. Steve Tilford from Steve’s Astro Corner knew Elliot personally and has written a very nice retrospective on Elliot’s life.

Posted on by Anne Minard

‘Armada of Telescopes’ Captures Most Distant Galaxy Cluster Ever Seen

Hubble infrared image showing CL J1449+0856, the most distant mature cluster of galaxies found. Color data was added from ESO’s Very Large Telescope and the NAOJ’s Subaru Telescope. Credit: NASA, ESA, R. Gobat (Laboratoire AIM-Paris-Saclay, CEA/DSM-CNRS–)

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The galaxies above are among the oldest objects astronomers have ever laid eyes — er, telescopes — on, formed when the Universe was less than a quarter of its current age. In a new study out in the journal Astronomy & Astrophysics, a team of researchers has announced that they’ve used a fleet of the world’s most powerful telescopes to measure the distance from here to there.

And things look awfully familiar.

“The surprising thing is that when we look closely at this galaxy cluster it doesn’t look young — many of the galaxies have settled down and don’t resemble the usual star-forming galaxies seen in the early Universe,” said lead author Raphael Gobat of Université Paris Diderot in France.

The Very Large Telescope (VLT) at ESO's Cerro Paranal observing site in the Atacama Desert of Chile, consisting of four Unit Telescopes with main mirrors 8.2-m in diameter and four movable 1.8-m diameter Auxiliary Telescopes. The telescopes can work together, in groups of two or three, to form a giant interferometer, allowing astronomers to see details up to 25 times finer than with the individual telescopes. Credit: Iztok Boncina/ESO

Clusters of galaxies are the largest structures in the Universe that are held together by gravity. Astronomers expect these clusters to grow over time so that massive clusters would be rare in the early Universe. Although even more distant clusters have been seen, they appear to be young clusters in the process of formation, not settled mature systems.

The international team of astronomers used the powerful VIMOS and FORS2 instruments on ESO’s Very Large Telescope (VLT) to measure the distances to some of the blobs in a curious patch of very faint red objects first observed with the Spitzer space telescope. This grouping, named CL J1449+0856  for its position in the sky, had all the hallmarks of being a very remote cluster of galaxies. The results showed that we are indeed seeing a galaxy cluster as it was when the Universe was about three billion years old.

Once the team knew the distance to this very rare object, they looked carefully at the component galaxies using both Hubble and ground-based telescopes, including the VLT. They found evidence suggesting that most of the galaxies in the cluster were not forming stars, but were composed of stars that were already about one billion years old. This makes the cluster a mature object, similar in mass to the Virgo Cluster, the nearest rich galaxy cluster to the Milky Way.

Further evidence that this is a mature cluster comes from observations of X-rays coming from CL J1449+0856 made with ESA’s XMM-Newton space observatory. The cluster is giving off X-rays that must be coming from a very hot cloud of tenuous gas filling the space between the galaxies and concentrated towards the center of the cluster. This is another sign of a mature galaxy cluster, held firmly together by its own gravity, as very young clusters have not had time to trap hot gas in this way.

As Gobat concludes, “These new results support the idea that mature clusters existed when the Universe was less than one quarter of its current age. Such clusters are expected to be very rare according to current theory, and we have been very lucky to spot one. But if further observations find many more then this may mean that our understanding of the early Universe needs to be revised.”

Source: ESO press release. The research appears in a paper, “A mature cluster with X-ray emission at z = 2.07,” by R. Gobat et al., published in the journal Astronomy & Astrophysics. (see also arxiv). Lead author’s affiliation page: Université Paris Diderot.

Posted on by Jon Voisey

STEREO Looks at the Sun; Finds Planets

STEREO spacecraft. Credit: NASA

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The primary mission of the twin STEREO probes is to explore the 3-dimensional makeup of our Sun. Each craft carries a variety of instruments. One of them, the Heliospheric Imager (HI), doesn’t look directly at the Sun, but rather, explores a wide field near the Sun in order to explore the physics of coronal mass ejections (CMEs), in particular, ones aimed at the Earth. But while not focusing on solar ejections, the HI is free to make many other observations, including its first detection of an extrasolar planet.

As the Heliospheric Imager stares at the space between the Earth and Sun, it has made many novel observations. The device first opened its shutters in 2006 the instrument has observed the interaction of CMEs with the atmosphere of Venus, the stripping of a tail of a comet by a CME, atomic iron in a comet’s tail, and “the very faint optical emission associated with so-called Corotating Interaction Regions (CIRs) in interplanetary space, where fast-flowing Solar wind catches up with slower wind regions.”

The spacecraft allows for long periods of time to stare at patches of sky as the satellites precede and follow Earth in its orbit. The spacecraft is able to take pictures roughly every 40 minutes for almost 20 days in a row giving excellent coverage. As a result, the images taken have the potential to be used for detailed survey studies. Such information is useful for conducting variable star studies and a recent summary of findings from the mission reported the detection of 263 eclipsing variable stars, 122 of which were not previously classified as such.

Another type of variable star observed by the STEREO HI, was the cataclysmic sort, in particular, V 471 Tau. This red giant/white dwarf binary in the Hyades star cluster is a strong source of interest for stellar astrophysicists because the system is suspected to be a strong candidate for a type Ia supernova as the red giant dumps mass onto its high mass, white dwarf companion. The star system is extremely erratic in its light output and observations could help astronomers understand how such systems evolve.

Although planetary hunting is at the very edge of the capabilities of the HI’s limitations, eclipses caused by planet sized objects are feasible for many of the brighter stars in the field of view as dim as approximately 8th magnitude. Around one star, HD 213597, the STEREO team reported the detection of an object that seems too small to be a star based on the light curve alone. However, follow up studies will be necessary to pin down the object’s mass more accurately.

Posted on by Tammy Plotner

Buckyballs… Throwing Astronomers A Curve

Artist's concept of buckyballs and polycyclic aromatic hydrocarbons around an R Coronae Borealis star rich in hydrogen. Credit: MultiMedia Service (IAC)

[/caption]When I first heard about buckyballs a couple of decades ago, I had nothing but the deepest respect for anyone who understood abstract ideas like string theory and branes. After all, how often were you likely to discuss Buckminster fullerenes with a contemporary while standing in the laundry detergent aisle of your local grocery store? The very concept of “magnetic” carbon was new and exciting! It was known to exist in small quantities in nature – produced by lightning and fire – but the real kicker was born solely in a laboratory. Buckyballs have been found on Earth and in meteorites, and now in space, and can act as “cages” to capture other atoms and molecules. Some theories suggest that the buckyballs may have carried to the Earth substances that make life possible.

According to the McDonald Observatory press release: Observations made with NASA’s Spitzer Space Telescope have provided surprises concerning the presence of buckminsterfullerenes, or “buckyballs,” the largest known molecules in space. A study of R Coronae Borealis stars by David L. Lambert, Director of The University of Texas at Austin’s McDonald Observatory, and colleagues shows that buckyballs are more common in space than previously thought. The research will appear in the March 10 issue of The Astrophysical Journal. The team found that “buckyballs do not occur in very rare hydrogen-poor environments as previously thought, but in commonly found hydrogen-rich environments and, therefore, are more common in space than previously believed,” Lambert says.

Buckyballs are made of 60 carbon atoms arranged in shape similar to a soccer ball, with patterns of alternating hexagons and pentagons. Their structure is reminiscent of Buckminster Fuller’s geodesic domes, for which they are named. These molecules are very stable and difficult to destroy. Richard Curl, Harold Kroto, and Richard Smalley won the 1996 Nobel Prize in chemistry for synthesizing buckyballs in a laboratory. The consensus based on lab experiments has been that buckyballs do not form in space environments that have hydrogen, because the hydrogen would inhibit their formation. Instead, the idea has been that stars with very little hydrogen but rich in carbon — such as the so-called “R Coronae Borealis stars” — provide an ideal environment for their formation in space.

Lambert, along with N. Kameswara Rao of Indian Institute of Astrophysics and Domingo Anibal García-Hernández of the Instituto de Astrofisica de Canarias, put these theories to the test. They used Spitzer Space Telescope to take infrared spectra of R Coronae Borealis stars to look for buckyballs in their chemical make-up. They found these molecules do not occur in those R Coronae Borealis stars with little or no hydrogen, an observation contrary to expectation. The group also found that buckyballs do exist in the two R Coronae Borealis stars in their sample that contain a fair amount of hydrogen. Studies published last year, including one by García-Hernández, showed that buckyballs were present in planetary nebulae rich in hydrogen. Together, these results tell us that fullerenes are much more abundant than previously believed, because they are formed in normal and common “hydrogen-rich” and not rare “hydrogen-poor” environments.

The current observations have changed our understanding of how buckyballs form. It suggests they are created when ultraviolet radiation strikes dust grains (specifically, “hydrogenated amorphous carbon grains”) or by collisions of gas. The dust grains are vaporized, producing an interesting chemistry where buckyballs and polycyclic aromatic hydrocarbons are formed. (The latter molecules of a variety of sizes are formed from carbon and hydrogen.) “In recent decades, a number of molecules and diverse dust features have been identified by astronomical observations in various environments. Most of the dust that determines the physical and chemical characteristics of the interstellar medium is formed in the outflows of asymptotic giant branch stars and is further processed when these objects become planetary nebulae.” says Jan Cami (et al). “We studied the environment of Tc 1, a peculiar planetary nebula whose infrared spectrum shows emission from cold and neutral C60 and C70. The two molecules amount to a few percent of the available cosmic carbon in this region. This finding indicates that if the conditions are right, fullerenes can and do form efficiently in space.”

Posted on by Anne Minard

Dusty Neighbor NGC 247 is a Million Light-Years Closer Than Thought

Spiral galaxy NGC 247, shot with the Wide Field Imager at ESO’s La Silla Observatory in Chile. Credit: ESO

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One of our celestial neighbors, the spiral galaxy NGC 247, just moved about a million light-years closer.

Well, not really. But astronomers are retooling estimates of the distance to it, which was overestimated in the past partly because of the nearly edge-on tilt, shown above. The just-released image, from the Wide Field Imager on the MPG/ESO 2.2-metre telescope in Chile, shows large numbers of the galaxy’s component stars and glowing pink clouds of hydrogen, marking regions of active star formation, in the loose and ragged spiral arms. Numerous other galaxies can be seen in the distance.

Through a moderate-sized amateur telescope, the Cetus galaxy appears large but dim, and is seen best in a dark sky. Credit: ESO, IAU and Sky & Telescope

NGC 247 (RA 00h 47′ 14″  – 20deg 52′ 04″) is one of the closest spiral galaxies of the southern sky, now believed to lie about 11 million light-years away in the constellation Cetus (The Whale). It’s part of the Sculptor Group, a collection of galaxies associated with the Sculptor Galaxy (NGC 253, shown in previous releases here and here). This is the nearest group of galaxies to our Local Group, which includes the Milky Way.

To measure the distance from the Earth to a nearby galaxy, astronomers have to rely on a type of variable star called a Cepheid to act as a distance marker. Cepheids are very luminous stars, whose brightness varies at regular intervals. The time taken for the star to brighten and fade can be plugged into a simple mathematical relation that gives its intrinsic brightness. When compared with the measured brightness this gives the distance. However, this method isn’t foolproof, as astronomers think this period–luminosity relationship depends on the composition of the Cepheid.

Another problem arises from the fact that some of the light from a Cepheid may be absorbed by dust en route to Earth, making it appear fainter, and therefore further away than it really is. This is a particular problem for NGC 247 with its highly inclined orientation, as the line of sight to the Cepheids passes through the galaxy’s dusty disc.

However, a team of astronomers is currently looking into the factors that influence these celestial distance markers in a study called the Araucaria Project. The team has already reported that NGC 247 is more than a million light-years closer to the Milky Way than was previously thought, bringing its distance down to just over 11 million light-years.

More information about the lead image: It was created from a large number of monochrome exposures taken through blue, yellow/green and red filters taken over many years. In addition, exposures through a filter that isolates the glow from hydrogen gas have also been included and colored red. The total exposure time per filter was 20 hours, 19 hours, 25 minutes and 35 minutes, respectively.

Source: ESO press release. The paper appears here. See also the website for the Araucaria Project.

Posted on by Nancy Atkinson

What’s Up for March?

Jane Houston Jones from JPL provides a video report on the happenings in space this month, and what you can see in the night sky in March: the MESSENGER spacecraft goes into orbit around Mercury on the 18th, and you can see the swift planet in the evening skies, too! Meanwhile, celebrate Sun-Earth day on the 19th, and view the sun through solar safe telescopes.

Jones was also featured on a recent 365 Days of Astronomy podcast, talking with Jane Platt and providing a “Sneak Peek at the Springtime Skies.”

Posted on by Jon Voisey

Another Ceasing Cepheid

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Earlier this year, I wrote an article about a Cepheid variable star named V19 in M31. This Cepheid was one that once pulsated strongly and was one of the variables Hubble first used to find the distance to the Andromeda galaxy. But today, V19 is a rare instance of a Cepheid that has seemingly, stopped pulsating. Another example of this phenomenon is that of Polaris, which has decreased in the amplitude of brightnesses by nearly an order of magnitude in the past century, although some reports indicate that it may be beginning to increase again. Meanwhile, a new paper is looking to add another star, HDE 344787, to this rare category and according to the paper, it may be “even more interesting than Polaris”.

The star in question, HDE 344787, is a F class supergiant. Although the variations in brightness have been difficult to observe, due to their small amplitude, astronomers have revealed two fundamental pulsation modes corresponding to 5.4 days and 3.8 days. But perhaps even more interesting, is that the 5.4 day period seems to be growing. Careful analysis of the data suggests that this period is growing by about 13 seconds per year. This finding is in strong agreement with what is predicted by models of stellar evolution for stars with metallicity similar to the sun passing through the instability strip for the first time.

HDE 344787 is similar in Polaris in that both stars share the same spectral type. However, the existence of two modes of pulsation is not seen in Polaris. The lengthening of the period of pulsation, however, is seen. For Polaris, its variation is growing by 4.5 seconds per year. Another similarity is that, like Polaris and V19, has been decreasing in the amplitudes of its brightness since at least 1890.

While the addition of this star to the collection of Cepheids that have decreased their amplitude, it does little to solve the mystery of why they might do so. Currently, both Polaris and HDE 344787 lie near the middle of the instability strip and, as such, are not simply evolving out of the region of instability. However, the confirmation of second pulsational mode may lend support to the notion that a change in one of these modes may serve to dampen the other, creating an effect known as the Blazhko Effect.

Ultimately, this star will require further observations to understand its nature better. Due the the faintness of this star (~10th magnitude) as well as the small change in brightness from the pulsations and the dense stellar field on which it lies, observations have been notoriously challenging.

Posted on by Anne Minard

Meteorites Illuminate Mystery of Chromium in Earth’s Core

It’s generally assumed that the Earth’s overall composition is similar to that of chondritic meteorites, the primitive, undifferentiated building blocks of the solar system. But a new study in Science Express led by Frederic Moynier, of the University of California at Davis, seems to suggest that Earth is a bit of an oddball.

 

 

Thin section of a chondritic meteorite. Credit: NASA

Moynier and his colleagues analyzed the isotope signature of chromium in a variety of meteorites, and found that it differed from chromium’s signature in the mantle.

“We show through high-precision measurements of Cr stable isotopes in a range of meteorites, which deviate by up to ~0.4‰ from the bulk silicate Earth, that Cr depletion resulted from its partitioning into Earth’s core with a preferential enrichment in light isotopes,” the authors write. “Ab-initio calculations suggest that the isotopic signature was established at mid-mantle magma ocean depth as Earth accreted planetary embryos and progressively became more oxidized.”

Chromium’s origins. New evidence suggests that, in the early solar nebula (A), chromium isotopes were divided into two components, one containing light isotopes, the other heavy isotopes. In the early Earth (B), these components formed a homogeneous mixture. During core partitioning (C), the core became enriched with lighter chromium isotopes, and the mantle with heavier isotopes. Courtesy of Science/AAAS

The results point to a process known as “core partitioning,” rather than an alternative process involving the volatilization of certain chromium isotopes so that they would have escaped from the Earth’s mantle. Core partitioning took place early on Earth at high temperatures, when the core separated from the silicate earth, leaving the core with a distinct composition that is enriched with lighter chromium isotopes, notes William McDonough, from the University of Maryland at College Park, in an accompanying Perspective piece.

McDonough writes that chromium, Earth’s 10th most abundant element, is named for the Greek word for color and “adds green to emeralds, red to rubies, brilliance to plated metals, and corrosion-proof quality to stainless steels.” It is distributed roughly equally throughout the planet.

He says the new result “adds another investigative tool for understanding and documenting past and present planetary processes. For the cosmochemistry and meteoritics communities, the findings further bolster the view that the solar nebula was a heterogeneous mixture of different components.”

Source: Science. The McDonough paper will be published online today by the journal Science, at the Science Express website.

Posted on by Anne Minard

T Chamaeleon Gets Caught in the Act — Forming Planets, That Is

Artist’s impression showing the disc around the young star T Chamaeleontis. The companion object in the foreground may be either a brown dwarf or a large planet. Credit: ESO/L. Calçada

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An international team of astronomers peering at a young star in the constellation Chamaeleon have detected a smaller companion — a dust-shrouded brown dwarf, or perhaps a planet — that appears to be carving out a large gap in the stellar disk. The discovery is a first: Although planets have been spotted before in more mature disks, this is the first detection of a planet-sized object in the disk around a young star.

Planets form from the disks of material around young stars, but the transition from dust disk to planetary system is rapid and few objects are caught during this phase. Astronomers are getting ever closer to glimpsing the births of planets, though — today’s announcement comes on the heels of a discovery last week using the Subaru Telescope in Hawaii, of a stellar disk around the star LkCa 15 similar in size to our own solar system, featuring rings and gaps possibly associated with the formation of giant planets.

T Chamaeleontis (RA 1h 04m 09.131s dec -76° 27′ 19.30″), T Cha for short, is a faint, young but sun-like star in the small southern constellation of Chamaeleon, about 350 light-years from Earth. T Cha is about seven million years old.

This chart shows the location of the young star T Cha within the constellation of Chamaeleon. The map shows most of the stars visible to the unaided eye under good conditions and the star itself is marked as a red circle. This star is too faint to see with the unaided eye, but is easily seen with a small telescope. Credit: ESO, IAU and Sky & Telescope

“Earlier studies had shown that T Cha was an excellent target for studying how planetary systems form,” said Johan Olofsson of the Max Planck Institute for Astronomy in Heidelberg, Germany, one of the lead authors of two related papers in the journal Astronomy & Astrophysics. “But this star is quite distant and the full power of the Very Large Telescope Interferometer was needed to resolve very fine details and see what is going on in the dust disk.”

The astronomers first observed T Cha using the AMBER instrument and the VLT Interferometer (VLTI). They found that some of the disk material formed a narrow dusty ring only about 20 million kilometers (12.4 million miles) from the star. Beyond this inner disk, they found a region devoid of dust with the outer part of the disk stretching out into regions beyond about 1.1 billion kilometers (683.5 million miles) from the star.

The ESO Very Large Telescope. Credit: ESO/G. Lombardi

“For us the gap in the dust disk around T Cha was a smoking gun,” said Nuria Huélamo, of the Centro de Astrobiología, ESAC in Spain, lead author of the second paper, “and we asked ourselves: could we be witnessing a companion digging a gap inside its protoplanetary disk?”

After further analysis, the team found the clear signature of an object located within the gap in the dust disk, about one billion kilometers, or 621 million miles, from the star — slightly further out than Jupiter is from our own sun.

The astronomers searched for the companion using NACO in two different spectral bands — at around 2.2 microns and 3.8 microns. The companion is only seen at the longer wavelength, which means that the object is either cool, like a planet, or a dust-shrouded brown dwarf.

Huélamo said he hopes future observations will reveal more about the companion and the disk, and explain what fuels the inner dusty disk.

Source: ESO press release. This research is presented in two papers to appear in the journal Astronomy & Astrophysics: Olofsson et al. 2011, “Warm dust resolved in the cold disk around TCha with VLTI/AMBER,” and Huélamo et al. 2011, “A companion candidate in the gap of the T Cha transitional disk.”

Posted on by Anne Minard

Close Look at Cas A Reveals Bizarre ‘Superfluid’

Credit: X-ray: NASA/CXC/UNAM/Ioffe/D. Page, P. Shternin et al.; Optical: NASA/STScI; Illustration: NASA/CXC/M. Weiss

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NASA’s Chandra X-ray Observatory has discovered the first direct evidence for a superfluid, a bizarre, friction-free state of matter, at the core of a neutron star.

The image above, released today, shows X-rays from Chandra (red, green, and blue) and optical data from Hubble (gold) of Cassiopeia A, the remains of a massive star that exploded in a supernova. The evidence for superfluid has been found in the dense core of the star left behind, a so-called neutron star. The artist’s illustration in the inset shows a cut-out of the interior of the neutron star, where densities increase from the orange crust to the red core and finally to the inner red ball, the region where the superfluid exists.

Superfluids created in laboratories on Earth exhibit remarkable properties, such as the ability to climb upward and escape airtight containers. When they’re made of charged particles, superfluids are also superconductors, and they allow electric current to flow with no resistance. Such materials on Earth have widespread technological applications like producing the superconducting magnets used for magnetic resonance imaging [MRI].

Two independent research teams have used Chandra data to show that the interior of a neutron star contains superfluid and superconducting matter, a conclusion with important implications for understanding nuclear interactions in matter at the highest known densities. The teams publish their research separately in the journals Monthly Notices of the Royal Astronomical Society Letters and Physical Review Letters.

Cas A (RA 23h 23m 26.7s | Dec +58° 49′ 03.00) lies about 11,000 light-years away. Its star exploded about 330 years ago in Earth’s time-frame. A sequence of Chandra observations of the neutron star shows that the now compact object has cooled by about 4 percent over a ten-year period.

“This drop in temperature, although it sounds small, was really dramatic and surprising to see,” said Dany Page of the National Autonomous University in Mexico, leader of one of the two teams. “This means that something unusual is happening within this neutron star.”

Neutron stars contain the densest known matter that is directly observable; one teaspoon of neutron star material weighs six billion tons. The pressure in the star’s core is so high that most of the charged particles, electrons and protons, merge — resulting in a star composed mostly of neutrons.

The new results strongly suggest that the remaining protons in the star’s core are in a superfluid state and, because they carry a charge, also form a superconductor.

Both teams show that the rapid cooling in Cas A is explained by the formation of a neutron superfluid in the core of the neutron star within about the last 100 years as seen from Earth. The rapid cooling is expected to continue for a few decades, and then it should slow down.

“It turns out that Cas A may be a gift from the Universe because we would have to catch a very young neutron star at just the right point in time,” said Page’s co-author Madappa Prakash, from Ohio University. “Sometimes a little good fortune can go a long way in science.”

The onset of superfluidity in materials on Earth occurs at extremely low temperatures near absolute zero, but in neutron stars, it can occur at temperatures near a billion degrees Celsius. Until now there was a very large uncertainty in estimates of this critical temperature. This new research constrains the critical temperature to between one half a billion to just under a billion degrees.

Cas A will allow researchers to test models of how the strong nuclear force, which binds subatomic particles, behaves in ultradense matter. These results are also important for understanding a range of behavior in neutron stars, including “glitches,” neutron star precession and pulsation, magnetar outbursts and the evolution of neutron star magnetic fields.

Sources: Press releases from the Royal Astronomical Society and Harvard. See additional multimedia at NASA’s Chandra page, and the two studies in MNRAS and Phys. Rev. Letters.